Quick answer
The Atlantic horseshoe crab is an ancient marine arthropod that has existed for hundreds of millions of years, making it a true living fossil. Despite its name it is not a crab but is more closely related to spiders and scorpions, with a horseshoe-shaped shell, many legs, and a long spike-like tail. Its copper-based blue blood is vital to medicine, and these animals can live more than 20 years.
Key takeaway
The Atlantic horseshoe crab is an ancient marine arthropod that has existed for hundreds of millions of years, making it a true living fossil. Despite its name it is not a crab but is more closely related to spiders and scorpions, with a horseshoe-shaped shell, many legs, and a long spike-like tail. Its copper-based blue blood is vital to medicine, and these animals can live more than 20 years.
Overview
The Atlantic horseshoe crab is an ancient marine arthropod that has existed for hundreds of millions of years, making it a true living fossil. Despite its name it is not a crab but is more closely related to spiders and scorpions, with a horseshoe-shaped shell, many legs, and a long spike-like tail. Its copper-based blue blood is vital to medicine, and these animals can live more than 20 years.
Biology
Atlantic Horseshoe Crab (Limulus polyphemus) is classified as Invertebrate with conservation status Vulnerable. Typical weight about 2 kg; lifespan around Often 20+ years.
Ecology
Diet: Omnivore (worms, mollusks, algae, carrion). Habitat: Shallow coastal waters and sandy beaches. Movement and social systems reflect those pressures.
People and this species
Learn before you travel or keep related pets. Wild individuals are not toys; captive care needs species-specific husbandry.
Further reading
See the full Atlantic Horseshoe Crab profile for FAQs, taxonomy, and related guides on this site.
An ancient survivor
Horseshoe crabs are among the oldest animal lineages still living, with fossil relatives dating back hundreds of millions of years, long before the dinosaurs. Their basic body plan has changed remarkably little over that time. Despite the name, they are not true crabs but chelicerates, the same broad group that includes spiders and scorpions.
Body and senses
A horseshoe crab has a smooth, domed shell, several pairs of legs hidden underneath, and a long, pointed tail called a telson that it uses to flip itself upright rather than as a weapon. It has up to ten eyes spread across its body, including large compound eyes used to find mates. The tail and shell are harmless to people despite their fierce appearance.
Diet and spawning
Horseshoe crabs are omnivores that plow through sand and mud searching for worms, mollusks, algae, and carrion, crushing food with the bases of their legs. Each spring, huge numbers gather on beaches to spawn, with females laying thousands of eggs in the sand. These eggs are a critical food source for migrating shorebirds along the Atlantic coast.
Blue blood and conservation
Horseshoe crab blood is blue because it uses copper-based hemocyanin instead of iron-based hemoglobin to carry oxygen. The blood contains a clotting agent used worldwide to test medicines and vaccines for dangerous bacterial contamination, making these animals important to human health. Overharvesting for bait and biomedical use, along with habitat loss, has led to the species being listed as Vulnerable.
Research notes
Figures for atlantic horseshoe crabs (Limulus polyphemus) come from field studies, museum records, and conservation assessments that do not always agree on exact averages. Prefer ranges over single-point claims, and check whether a source describes wild, captive, or mixed populations.
Practical takeaways
If you encounter atlantic horseshoe crabs in the wild, prioritise distance and local guidance. If you care for related domestic or captive animals, match diet and housing to species needs rather than generic pet advice. Share accurate status information (Vulnerable) when discussing conservation.
Sources
FAQs
Atlantic Horseshoe Crab: Key Facts & Natural History?
The Atlantic horseshoe crab is an ancient marine arthropod that has existed for hundreds of millions of years, making it a true living fossil. Despite its name it is not a crab but is more closely related to spiders and scorpions, with a horseshoe-shaped shell, many legs, and a long spike-like tail. Its copper-based blue blood is vital to medicine, and these animals can live more than 20 years.
What is the scientific name of the atlantic horseshoe crab?
Limulus polyphemus
What do atlantic horseshoe crabs eat?
Omnivore (worms, mollusks, algae, carrion)
Where do atlantic horseshoe crabs live?
Shallow coastal waters and sandy beaches
Are atlantic horseshoe crabs endangered?
Listed here as Vulnerable. Check IUCN and national lists for the latest assessment.